Thermal interfaces are widely used in heat dissipating applications where excess thermal energy is desired to be transferred from one location to another. The thermal interface is commonly positioned between such locations in a manner to accommodate the desired heat transfer in an efficient and mechanically useful manner. Example applications of such thermal interfaces is in the electronics industry, wherein electronic devices must be cooled in some fashion in order to maintain minimum threshold performance characteristics. A common method of cooling such electronic devices is through heat dissipation away from the heat-generating electronic devices. Such heat dissipation may be accomplished, for example, by thermally coupling the electronic device to a heat sink, which typically possesses a relatively high thermal dissipation capacity. Common heat sinks exhibit high heat dissipation characteristics through features such as materials, surface area, and exposure to cooling media.
Thermal coupling of heat-generating elements, such as electronic devices, to heat sinks may be facilitated by thermal interface materials and structures. For example, direct physical coupling between a heat-generating element and a heat sink may be difficult due to relative external geometries, materials, and spatial restrictions in the vicinity of the heat-generating element. In this case, thermal interfaces can act as the physical connection mechanism between the heat-generating element and the heat sink without significant impedance to heat transfer. Moreover, because heat transfer can be significantly impeded at thermal barriers where thermal energy must pass through media of relatively low thermal conductivity, thermal interfaces can increase the efficiency of heat transfer to a heat sink by minimizing the presence of thermal barriers. For example, thermal interfaces having relatively low modulus values can “conform” to surface irregularities in the heat-generating element and the heat sink, thereby minimizing and/or eliminating voids between surfaces that can be filled with relatively low thermal conductivity media such as air. Consequently, thermal interfaces have been found to significantly enhance heat transfer away from a variety of heat-generating devices.
In some applications, thermal interfaces have utilized relatively low modulus materials such as microcrystalline waxes, and silicone greases, gels, and waxes, in order to provide a “conformability” characteristic to the thermally conductive interface. Conformability of the interface may be achieved through materials having low modulus values at room temperature, or may instead be achieved as a result of a “phase changing” material which significantly softens at temperatures at or below the operating temperatures of the heat-generating devices to which the interface is coupled. The relative softness of the interface material can result in a surface tackiness that hinders such handling of such interfaces, such as in assembly of the thermal interfaces to respective components.
To overcome this problem, it has been found that the provision of an “anti-blocking” or release layer formed on at least one outer surface of the thermal interface assists production, assembly, and handling of the thermal interface. Moreover, such an outer non-tacky release layer serves to provide significant protection against contamination to the remainder of the thermal interface. In some cases, the anti-blocking or release layer may comprise a liner film that must be removed prior to the point in time when the thermal interface is placed into contact with the heat-generating device. This removal operation has frequently proven to be bothersome, and is time consuming and labor intensive. In other cases, the anti-blocking or release layer may be integrally formed, or permanently secured to, the remainder of the thermal interface. In such cases, however, the anti-blocking layer significantly inhibits the overall conformability of the interface.
In addition to the above, thermal interfaces are routinely installed in heat dissipation arrangements in a specific order in which the thermal interface is first secured to the heat sink, with the resultant combination then secured to a previously constructed package, such as an integrated circuit board. This protocol has been followed primarily due to the fact that mounting the thermal interface to components of an electronic package in its construction process is difficult and messy to handle. Even for thermal interfaces with anti-blocking layers, temperatures reached in solder reflow processes to secure electronic components to the package compromise the effectiveness of the anti-blocking layer.
In view of the above, therefore, it is a principal object of the present invention to provide a thermal interface incorporating one or more highly thermally conductive surfaces which remain non-tacky at or above solder reflow temperatures, while also enabling good overall conformability to adjacent surfaces.
It is a further object of the present invention to provide a thermal interface member having a non-tacky surface layer that is highly thermally conductive, conformable, and remains non-tacky at or above solder reflow temperatures.
It is another object of the present invention to provide a method for constructing a thermal interface, wherein the surface layer of such interface is deposited on a release substrate and subsequently placed in registration with a bulk layer of the interface.
It is a still further object of the present invention to provide a method for constructing a package by securing a thermal interface to a package component prior to solder reflow, and subsequently securing the combination to a heat sink.